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Seismic Imaging

A Review of the Techniques, their Principles, Merits and Limitations (EET 4)

image of Seismic Imaging
  • By Etienne Robein
  • Format: EPUB
  • Publication Year: 2010
  • Number of Pages: 244
  • Language: English
  • Ebook ISBN: 9789073834972

The book presents the various seismic imaging methods currently in use in the Oil and Gas industry in a unified and almost equation-free approach. Guided step by step through each method well illustrated by figures and examples, the reader will discover differences between time and depth imaging, how they impact the quality of the seismic image, the distinction between Kirchhoff, Gaussian Beam and other Beam techniques, principles of ray-based tomography and how it may be used after wave-equation methods, in what sense two-way Reverse Time Migration differs from one-way Shot Point migration, what are the emerging routes for migration velocity analysis, what can we expect from Full Waveform Inversion and at what cost, how 3D and wide azimuth acquisition impact imaging, and answers to many other questions.

Table of Contents

Cover
Title Page
Copyright Page
contents
Introduction – What is a reflection seismic image exactly?

What is a reflection seismic image exactly?
Transmission, attenuation, refraction and other primary reflections
Multiple reflections
Processing and imaging
Objective of seismic imaging

1 Wave propagation: some reminders
P-wave propagation
Measuring the elastic wave with hydrophones and geophones
Seismic amplitudes
The ‘wave equation’ and propagation velocity
The wave equation
Propagation velocity
Simulation of wave propagation – numerical modelling
Wavefront and rays
The subsurface is anisotropic
Wavefront, phase and group angles and velocities in anisotropic media
Analytical parameterization of velocity
Parameterization of velocity anisotropy
Snell’s law and rays in anisotropic media
Rays, wavefront and seismic record relationships

2 Principles of Ray-based and Kirchhoff summation migrations
Reflectors and diffractors in the Earth
The reflector model
Ray migration
The diffraction model
Kirchhoff summation concept
Some considerations on reflection and diffraction in Kirchhoff summation migration
Implementation of Kirchhoff summation migrations

3 Pre-stack time migrations: principles and velocity analysis
Definition of vertical time
Kirchhoff migration in the vertical time domain
The common offset domain
Diffractions and Kirchhoff summation in the common offset domain
Multi-offset imaging, common image gathers and stack
Derivation of the diffraction curve in PreSTM: the ray tracing approach
Derivation of the diffraction curve in PreSTM: the analytical approaches
PreSTM migration velocity analysis
Principle of RMO
Benefits and limitations of PreSTM

4 Ray-based Kirchhoff Migrations and Tomography
Principles of Kirchhoff PreSDM in the common-offset domain
Image domain-oriented versus data domain-oriented implementations
Tomographic inversion of image gathers
Different models to represent the anisotropic velocity field
Linearized tomography
CIG’s flatness and residual move-out analysis
Layer-based versus grid tomography
Velocity Model Building workstation
Constraints, well ties and regularization
Linear versus non-linear tomography
Migration operators in 3D
Kirchhoff migration seen from the reflector’s standpoint: reflection angle and other reflection-related CIGs
Diffraction imaging

5 Ray-based Beam Migrations
Concept of offset-ray migration of a reflection element from a shot gather
Offset-ray migration in the common-offset domain
Offset-ray migration of elements picked in the mid-point gather domain
Issues in 3D offset ray migration
Migration quality indicator
Tau-p transforms
Gaussian Beam Migration principles
GBM versus Kirchhoff migration: some comments
GBM key parameters
Controlled, beam-steer, wavelet-based, diplet-based and other ‘fast’ beam migrations
‘Controlled’ beam migrations
Wavelet-based migration
Diplet-based migrations in the common-offset domain
Events selection in Beam migration
Offset- and Angle-Common Image Gathers and velocity analysis in beam migrations
Advantages and limitations of ray-based beam migrations

6 Wavefield Extrapolation Migrations
The imaging principle
Imaging condition
Depth versus time extrapolation
Principles of one-way shot migration
Handling all shots
Wavefield extrapolation in hybrid Fourier + space domains
Delayed- and encoded-shot migrations
Concept of survey sinking
Principle and workflow of Reverse Time Migration
Handling all shots in RTM
Time extrapolation using a Finite Difference scheme
The RTM ‘noise’
Why RTM is a computer-intensive process and possible remedies
Recapitulation: benefits and drawbacks in RTM

7 Wavefield Extrapolation Migration Velocity Analysis and Inversion-based Techniques
The concept of Subsurface-Offset Common Image Gathers
Subsurface Offset- and Scattering Angle CIGs from several shots
SO-CIG and SA-CIG after RTM
SO- and SA-CIGS when the velocity model is not correct
Migration Velocity Analysis using Subsurface Offset CIGs
Impact of 3D acquisition on Subsurface Offset CIGs
Principle of Full Waveform Inversion
The forward problem in FWI
The workflow of FWI in the frequency domain
Laplace-Fourier domain and the initial model
Plane-wave and encoded shot approaches
The Valhall 3D example

8 Examples, Discussion and Conclusion
Some considerations on resolution of Migration and Full Waveform Inversion
Migration, Least Squares Migration and Full Waveform Inversion
Beyond conventional seismic imaging
Double Focusing
CRS stack and Multi-focusing
Ray tracing as a tool for ‘geophysical interpretation’ while imaging
Imaging with prism waves
Anisotropy model: VTI or STI?
Anisotropy parameters: how to obtain ε and δ?
Azimuthal velocity anisotropy
Is there an optimum algorithm for imaging?
Imaging is team work and geological input is of particular importance
As a conclusion …

9 Acknowledgements
10 References
Text books and general interest papers
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8

11 Index

References

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